The modern communications era has brought about a tremendous proliferation of wireline and wireless networks. Computer networks, television networks, and telephony networks in particular are experiencing an unprecedented technological expansion, fueled by consumer demand. The ever-increasing need for bandwidth has exceeded even the most perspicacious expectations, as the explosion of data and multimedia transmissions are breaking the seams of the networking infrastructure. This has propelled a fervent effort to quickly increase the available communications bandwidth.
In line with this effort, various data transmission technologies have been employed and improved upon. Improved networking architectures and protocols over copper wires, radio waves and fiber-optic cable are helping in the effort to increase available bandwidth. Of late, optical data communication over the fiber-optic infrastructure is proving to be one of the most promising areas to assist in this effort. The fiber-optic cabling laid over the last couple of decades have traditionally been underused with respect to bandwidth. Essentially, this has been due to the failure to multiplex signals on a given fiber. For example, the first major use of optical fiber was a single-mode use where a single signal is transmitted through the fiber. In this mode, service providers quickly experience fiber exhaustion such that bandwidth can no longer be increased unless more fibers are installed.
Efforts have now turned to modulation techniques used to transmit the optical signals. In order to increase bandwidth, wavelength division multiplexing (WDM) has been used to allow multiple signals to travel along a single fiber. Wavelength division multiplexing (WDM) is a technique where multiple signals having different wavelengths are launched on the same fiber and demultiplexed at the receiving end. Each optical signal is assigned to a frequency (wavelength) within a designated frequency band, and the individual signals are multiplexed onto a single fiber where they can be collectively amplified. The first such use was to allow two different signals at two different wavelengths to travel along a fiber, which essentially doubled the bandwidth available for each fiber. The original two-wavelength mode communicated optical signals at about 1300 nm and 1550 nm. This additional bandwidth, while beneficial, was very quickly devoured by the unforeseeably immense demand for bandwidth. It became apparent that further increases in bandwidth capacity would be necessary.
It was determined that single-fiber bandwidth could be increased by further increasing the number of wavelength-modulated signals transmitted through the fiber. This effort has had some success using WDM technology, and is generally referred to as dense WDM (DWDM). However, dense multiplexing techniques for smaller wavelength spacings are more difficult to manufacture. Further, the current thrust is the realization of true optical networking. Such a network utilizes optical cross-connects and amplifiers to transmit optical signals over long distances without the need for electrical regeneration. More particularly, the Erbium-doped fiber amplifier (EDFA) allows for direct amplification of an optical signal without the need for intermediate electronic circuitry. EDFAs are pieces of optical fibers doped with the rare earth element erbium, an element that passively amplifies light in the 1550 nm region when pumped by an external light source. However, commercially-available EDFAs operate in a specific frequency band, and do take advantage of the entire optical communication band.
Current networks incorporating optical transmission are not necessarily fully-optical networks, and incorporate SONET (Synchronous Optical NETwork) or SDH (Synchronous Digital Hierarchy) nodes. Point-to-point data transfers may be made via fiber, but switching and/or amplifying functions are performed using digital switching and amplification technologies. Therefore, data networks employing optical transmission may also be required to operate in connection with existing electronic switching nodes.
Protection strategies over WDM networks is also an important consideration. Network resilience is important to account for cable breaks or other impairments to fiber-optic communication. This is often accomplished by reserving a portion of the fibers in a particular configuration for restoration in the event of a working channel failure. For example, in a four-fiber bidirectional line-switched ring, half of the ring's capacity is reserved for optical survivability. Such protection is available for various network architectures, such as linear or optical ring architectures.
In view of the many considerations that must be accounted for in such networks, the challenge still remains to maximize the bandwidth and fully utilize the optical communications band. There is a need in the communications industry for a network node architecture that fully utilizes the optical communications band while providing various protections on the same mesh/ring network. The present invention provides a solution to these and other shortcomings of the prior art, and offers additional advantages over the prior art.